FIG. 3 is the system diagram showing an example of a configuration of a general thermal power plant described in Non Patent Literature 1 detailed below.
As shown in FIG. 3, a general thermal power plant is generally constructed from the boiler 2; the steam system 3; the condensate system 44; and the feed-water system 4. The boiler 2 generates the combustion gas and combustion heat by combusting fuel such as coal, oil, or the like; and generates steam by increasing a temperature of feed-water by using the combustion heat. The steam system 3 has multiple steam turbines 5 and the condenser 6. Each of the steam turbines 5 is driven by the steam generated by the boiler 2. The steam exhausted from the steam turbines 5 enters into the condenser 6 to be steam condensate. The steam condensate in the condenser 6 is returned back to the boiler 2 through the condensate system 44 and feed-water system 4. The condensate system 44 has the condensate pump 7 for supplying the steam condensate, the low-pressure feed-water heater 8 constituted from multiple heat exchangers, and the deaerator 9. The feed-water system 4 has the high-pressure feed-water heater 10 constituted from the boiler feed-water pump 45 and multiple heat exchangers.
FIG. 4 is an enlarged view of the region P shown in FIG. 3 and indicates an enlarged view of the configuration around the boiler in a conventional coal-fired power plant as an example of a general thermal power plant. As shown in FIG. 4, the conventional coal-fired power plant 101 has: the boiler 102; the steam system 103; the feed-water system 104; the exhaust gas system 111; the primary air system 112; and the secondary air system 113.
The exhaust gas system 111 has the catalytic NOx removal equipment 114; the regenerative air preheater 115; the dust collector 116; the induced draft fan 117; the sulfur removal equipment 118; and the chimney 119. This exhaust gas system 111 is the flue channeling the combustion gas exhausted from the boiler 102 as the exhaust gas to the chimney 119. The exhaust gas exhausted from the boiler 102 is sent to the regenerative air preheater 115 after passage through the NOx removal equipment 114. After exchanging heat with the air for transporting pulverized coal in the primary air system 112 (hereinafter referred as “the primary air”) and the air for combustion in the secondary air system 113 (hereinafter referred as “the secondary air”), the exhausted gas sent to the air preheater 115 passes through the dust collector 116; the induced draft fan 117; and the sulfur removal equipment 118, and is discharged into the atmosphere eventually.
The primary air system 112 has the primary air fan 120; the hot air damper 121; the bypass duct 122 to bypass the air preheater 115; the cold air damper 123 provided to the bypass duct 122; and the coal pulverizer 124. The primary air is produced by mixing the hot air, which is heated by heat exchanging with the exhaust gas from the boiler 102 in the air preheater 115, and the cold air, which provided from the bypass duct 122 bypassing the air preheater 115, by controlling each of openings of the hot air damper 121 and the cold air damper 123. Because of this, the air amount of the primary air is adjusted to the required amount for transporting the pulverized coal. In addition, temperature of the primary air at the inlet of the coal pulverizer 124 is adjusted to the required temperature. After above-described adjustments, the primary air is introduced into the coal pulverizer 124. The primary air introduced into the coal pulverizer 124 evaporates the moisture in the pulverized coal by using its potential heat; and transfers the dried pulverized coal to the pulverized coal burner provided to the boiler 102 to have the pulverized coal to be combusted. Although it is not depicted in the drawing, the fuel coal is supplied to the coal pulverizer 124 and pulverized to a predetermined grain size.
The secondary air system 113 has the forced draft fan 125. The secondary air is introduced into the air preheater 115 and heated by heat exchanging with the exhaust gas from the boiler 102. Then, the secondary air is introduced into the boiler 102 as the air for combustion by the pulverized coal burner and the air for the two staged combustion.
The feed-water system 104 has the deaerator 109; the boiler feed-water pump 145; the high-pressure feed-water heater 110; and the economizer 136. Between the intermediate-pressure steam turbine 105I and the deaerator 109, and between the intermediate-pressure steam turbine 105I and the high-pressure feed-water heater 110, the extraction system 129, and the extraction system 130 are provided, respectively. The extraction steam from the intermediate-pressure steam turbine 105I flows in both of the extraction systems 129, 130. In addition, between the high-pressure steam turbine 105H and the high-pressure feed-water heater 110, the steam extraction systems 131, 132 are provided. The extraction steam from the high-pressure steam turbine 105H flows in both of the extraction systems 131, 132. The drain pipes 133-135 are piping in which drain from the high-pressure feed-water heater flows.
The high-pressure feed-water heater 110 is consisted from multiple heat exchangers. They are referred as the first high-pressure feed-water heater 126; the second high-pressure feed-water heater 127; and the third high-pressure feed-water heater 128 based on their locations from the deaerator 109 for the sake of simplicity. Feed-water heated in the high-pressure feed-water heater 110 is sent to the economizer 136 in the boiler 102.
Each of heat exchangers of the high-pressure feed-water heater 110 heats feed-water by using the steam extracted from the intermediate-pressure steam turbine 1051 and the high-pressure steam turbine 105H. The extraction system 130 sends the extraction steam to the first high-pressure feed-water heater 126; the extraction system 131 sends the extraction steam to the second high-pressure feed-water heater 127; and the extraction system 132 sends the extraction steam to the third high-pressure feed-water heater 128. The extraction steam sent to the second and third high-pressure feed-water heaters 127, 128 becomes drain after heat exchanging with feed-water. This drain is sent to the first high-pressure feed-water heater 126 through the drain pipes 135, 134. In the first high-pressure feed-water heater 126, feed-water is heated by using the drain from the second high-pressure feed-water heater 127 and the extraction steam extracted from the extraction system 130. Then, the drain discharged from the first high-pressure feed-water heater 126 is sent to the deaerator 109 through the drain pipe 133.
The steam system 103 has the evaporator 137; the superheater 138; the high-pressure steam turbine 105H; the reheater 139; and the intermediate-pressure steam turbine 105I. Feed-water introduced from the feed-water system 104 to the economizer 136 in the boiler 102 becomes superheated steam by passage through the evaporator 137 and the superheater 138. Then, the superheated feed-water is introduced into the high-pressure steam turbine 105H. The exhaust steam from the high-pressure steam turbine 105H is re-introduced into the boiler 102 and channeled to intermediate-pressure steam turbine 105I after re-heating by the reheater 139.
Making a thermal power plant with a regenerative reheating cycle highly efficient has been promoted conventionally (refer Patent Literature 1). Obtaining a steam condition with high temperature and high pressure is a very important and fundamental factor contributing to improvement of its efficiency. In general, increasing the steam temperature at the inlet of the steam turbine is very effective measure to improve power generation efficiency. Under the present set of circumstances, it is believed that the upper limitation of the high temperature in the steam condition for the materials standardized for the materials of thermal power plant for electric power generation is around 630° C. To deal with temperature higher than the steam temperature, usage of Fi-Ni-based alloy steel, Ni-based alloy steel, or the like is needed.
However, the usage of these materials is still in a developing stage as the next generation of high temperature materials at this time, since there are plenty of problems to be solved, such as their manufacturability and material properties, in the usage of these materials. In addition, these materials are more expensive than the currently standardized materials. Thus, usage of these materials becomes an economical problem during actual plant construction. Therefore, a highly efficient thermal power plant not relying on these high temperature materials has been desired.
Furthermore, in the case where the selective catalytic reduction NOx removal equipment is used as shown in FIG. 4, there is a problem in which the acidic ammonium sulfate is precipitated and the performance of the denitrification catalyst is reduced when the exhaust gas temperature at the inlet 114a of the NOx removal equipment 114 is low. In order to prevent this problem, it has to be operated in such a way that the exhaust gas temperature at the inlet 114a of the NOx removal equipment 114 is a high temperature free of the acidic ammonium sulfate precipitation. In other words, increasing a temperature of feed-water by increasing the heat-transfer area of the economizer 136 in order to reduce the temperature of the exhaust gas from the boiler, causes reduction of the denitrification performance in the early stage due to the reduction of the inlet gas temperature of the NOx removal equipment 114. Because of this, there is a problem that recovery of the exhaust gas temperature by the economizer 136 cannot be done sufficiently.
Furthermore, while the exhaust gas after passage through the NOx removal equipment 114 is subjected to heat exchanging with the primary air and the secondary air in the regenerative air preheater 115, there is a limitation for the temperature effectiveness of the air preheater 115. Therefore, the exhaust gas is released into the atmosphere from the chimney in the state where the potential heat of the exhaust gas from the boiler is not sufficiently recovered in the actual situation.
In addition, as shown in FIG. 4, the temperature of the primary air is controlled to be the required temperature in the inlet of the coal pulverizer 124 by controlling the mixing amounts of the hot air and the cold air in the conventional coal-fired power plant 101. However, the cold air does not contribute to the heat exchanging with the exhaust gas in the air preheater 115. Thus, there is a problem that heat exchanging between the combustion air (the primary air and the secondary air) and the exhaust gas from the boiler is not performed in the maximum efficient.